Molded loudspeaker diaphragm

ABSTRACT

A loudspeaker diaphragm is formed by dipping a suitably-shaped mold into a fibrous slurry. After drying, there is provided a diaphragm having a frusto-conical body and a flange arranged to be fixedly mounted. The diaphragm is then laterally compressed. When a driver mechanism is coupled to the smaller end of the body and is energized, the flange is repetitively flexed. The flange is capable of withstanding substantial and prolonged flexing by virtue of having been compressed during the construction thereof.

[ 1 Oct. 30, 1973 3,253,970 5/1966 Williams 156/228 MOLDED LOUDSPEAKER DIAPHRAGM Inventor: Fred D. Yocum, Jack Oak St.,

Cassville, Wis. 53806 Sept. 23, 1971 Primary Examiner-Stephen J. Tomsky Attorney-Harold V. Stotland [22] Filed:

ABSTRACT Appl. No.: 183,135

[52] U S Cl Isl/32 R A loudspeaker diaphragm is formed by dipping a suitably-shaped mold into a fibrous slurry. After drying,

there is provided a diaphragm having a frusto-conical 181/32 R r 4 0 H 0 0 3 l k 0 l G Int. [58] Field of body and a flange arranged to be fixedly mounted. The diaphragm is then laterally compressed. When a [56] References Cited UNITED STATES PATENTS driver mechanism is coupled to the smaller end of the body and is energized, the flange is repetitively flexed. The flange is capable of withstanding substantial and prolonged flexing by virtue of having been compressed during the construction thereof.

1 Claim, 9 Drawing Figures PATENTEDnm 30 I975 SHEET 1 [1F 2 FIGJ PATENTED BU 30 I975 SHEET 2 u; 2

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AV A'W/ FIG. 8

fiiiiii'l FIG MOLDED LOUDSPEAKER DIAPHRAGM BACKGROUND OF THE INVENTION In a direct radiator type of moving-conductor loudspeaker, there is provided a diaphragm including a body having a frusto-conical shape, with a flange on the larger end of the body. The flange is secured to a housing, which housing also carries a driver mechanism mechanically coupled to the smaller end of the diaphragm body. When the driver is energized, the diaphragm vibrates at the frequency of the cnergization signal. The resonant frequency of the diaphragm is the frequency at which the diaphragm vibrations are the greatest. In order to achieve good reproduction of low frequency tones, it is desirable to so construct the diaphragm that the resonant frequency is as low as possible.

In the past, in order to reduce the resonant frequency, it has been common to shave material from the flange portion of the diaphragm. Since the flange,

, which usually has rolls therein, functions much like a hinge between the frusto-conical body of the flange and the mounting means therefor, the thinner diaphragm facilitates the bending action of that flange. The entire diaphram is not made thinner initially, since that would cause the body to have insufficient rigidity to be self-supporting.

Although the shaving of the flange had the desired effect of reducing the resonant frequency, it also undesirably lessened the useful life of the diaphragm. In installations where the diaphram would be subjected to extensive use, or in an environment in which it was subjected to extensive jostling or the like, the shaved flange would tear, crack, or otherwise become damaged.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to prolong the life of a molded loudspeaker diaphragm that is extensively used and/or used in an environment in which it is subjected to substantial jostling.

It is another object to provide an improved, molded loudspeaker diaphragm formed first by dipping a suitably-shaped mold into a slurry, followed by a drying process, and then subjecting the thus formed member to a substantial pressure.

Another object is to apply a lacquer or other hardening agent to a molded loudspeaker diaphragm which has been compressed, thereby retaining the diaphram in its compressed state. I

In summary, there is provided a loudspeaker diaphram of a compressible material and comprising a body having a frusto-conical shape with a larger end and a smaller end coupled in use to a driver, a flange on the larger end and adapted to be fixedly mounted in use, the flange having been laterally compressed under a pressure of at least about lbs. per square inch, whereby said flange is capable of withstanding extensive and prolonged flexing thereof when the body is vibrated by the driver.

In another form of the invention there is provided an improved method of making a loudspeaker diaphragm, which method comprises the steps of providing a slurry including fibers in a liquid carrier, depositing the slurry on a diaphragm mold, drying the slurry to provide a member generally conforming to the shape of the mold, removing the member from the mold and compressing the member under a pressure of at least about 10 lbs. per square inch.

With the foregoing and other objects in view which will appear as the description proceeds, the invention consists of certain novel steps and certain features of construction, and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the steps and in the form, proportion, size, and minor details of the structure may be made without departing from the spirit or sacrificing any of the advantages of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawings a preferred embodiment thereof, from an inspection of which, when considered in connection with the following description, the invention, its mode of construction, assembly and operation, and many of its advantages should be readily understood and appreciated.

FIG. 1 is a cross-sectional view of a loudspeaker incorporating therein a loudspeaker diaphragm constructed in accordance with the features of the present invention;

FIG. 2 is a top plan view of the diaphragm;

FIG. 3 is a bottom plan view of the diaphragm;

FIG. 4 is a view in vertical section on an enlarged scale taken along the line 44 of FIG. 2;

FIG. 5 is a view in vertical section of a mold used in making the diaphragm shown in FIGS. 1-4 and a slurry deposited on such mold;

FIG. 6 is a fragmentary view on an enlarged scale of the mold and slurry shown in FIG. 5, with portions broken away to expose the various layers;

FIG. 7 is an enlarged view in vertical section showing the diaphragm member being blown from the mold;

FIG. 8 is a view of the diaphragm with a lacquer coating applied thereto; and

FIG. 9 is a view of a press consisting of two die members to compress the diaphragm.

Turning now to the drawings, and more particularly to FIG. 1 thereof, there is shown a loudspeaker 20 including a housing 21 which is round in outline, the housing 21 having a central portion 22 which is generally frusto-conically shaped, and a rear wall 23 disposed in a plane generally perpendicular to the axis of the central portion 22. Toward the front of the central portion 22 is a front wall 24 also located in a plane normal to the axis of the central portion 22. The outer end of the front wall 24 carries a forwardly-directed lip 25. Mounted on the rear wall 23 is a driver mechanism 26 including a field coil case 26a, which carries therein a field coil 27 wrapped about a" pole piece 28. Associated with the pole piece 28 is the usual voice coil 29. The

driver mechanism 26 is well-known in the art, whereby further details will not be given herein.

Also carried in the housing 21 is a diaphragm 40, the details of which will be described presently. The smaller end of the diaphragm 40 is attached to the voice coil 29, and the flange on the larger end of the diaphragm 40 abuts against the front wall 24. A ringshaped baffle gasket 30 fits inside the lip 25 and holds the outermost portion of the flange of the diaphragm 40 against the front wall 24 of the housing 21. There is also provided a dust cap 31 adjacent the smaller end of the diaphragm 40 to preclude dust from entering the driver mechanism 26.

Turning now to FIGS. 2-4, the details of construction of the diaphragm 40 will be described. The diaphragm 40 is constructed of a molded fibrous material, which fibers may be sulfites, sulfates, cotton, wool, kapok, combinations thereof, or other fibrous materials capable of being compressed. The diaphragm 40 includes a body 41 in the shape of the frustum of'a cone. In the particular form shown, the cone is one of revolution. However, it is to be understood that other conical shapes are contemplated, such as one in which the directrix is an ellipse. The smaller end of the body 41 terminates in a circular neck or apex 42 which has its axis common with the axis of the body 41. On approximately the lowermost half of the inside surface of the body 41 is a plurality of laterally spaced apart, circular ridges or ribs 43 (FIG. 3) which serve to rigidify the body 41. At the larger end of the body 41 is a flange 44 which is ring-like in form and isdefined by a plane that is normal to the axis of the body 41. On the innermost portion of the flange 44 is a plurality of annular undulations or rolls 45, the innermost one of which is a continuation of the body 41. The outermost portion 46 of the flange 44 is flat and is arranged to be disposed between the front wall 24 of the housing 21 and the gasket 30. Also, the voice coil 29 is mechanically coupled to the apex 42 of the diaphragm 40.

When the driver mechanism 26 is energized by virtue of an AC signal applied to the input conductors (now shown) of the field coil 27, the voice coil 29 will reciprocate at a frequency dependent upon the frequency of the signal. The'diaphragm 40, being connected to the voice coil 29, will be moved thereby in a piston-like motion, with the rolls 45 serving as a hinge or pivot to enable the body 41 to reciprocate with respect to the outermost portion 46 of the flange 44.

In order that the diaphragm 40 be capable of reproducing low frequency sounds, it is desirable that the resonant frequency of the diaphragm be low. By lessening the thickness of the material which makes up the rolls 45, the resonant frequency of the diaphragm 40 can be reduced. In the past, such reduction in thickness was accomplished by shaving material from the flange, or in the case of a molded diaphragm depositing less material in the flange region. However, the flexing of the rolls formed in such a flange would, after a certain periodof time, crack, tear or otherwise become damaged. 7 I I In the instant invention, on the other hand, the material making up the rolls 45 is compressed, as will be explained, so as greatly to lengthen the life of the dia-' phragm. I

' The diaphragm 40.,has a'coating oflacquer 47 or other hardening agent applied thereto. If desired, the hardening agent may be mixed in with the slurry. The lacquer 47 serves to retain the diaphragm 40 in its compressed state, to repel water and to affect the over-all frequency response, characteristic of the diaphragm 40. In the specific form shown, a lacquer of one concentration was applied over the body 41 and a lacquer of another concentration was applied to the flange '44. Pres-' sure was applied to the flange 44 and to the portion of all frequency response of the diaphragm 40 can be ad- -justed.

' Turning now to FIGS. 5-9, the method of making the diaphragm 40 will be described. There is provided a mold 50 which is round in outline and has a base 51 with an inlet opening 52. The mold also includes a body 54 in the shape of a frustrum of a cone. At the smaller.

end of the body 54 is a head; 55, and at the larger end of the body 54 is a ring-like flange 56 which is arranged to be substantially normal to the axis of the body 54. There are provided a number of air holes 57 in the body 54 and in the flange 56. There is also provided a screen 60 of very fine mesh and entirely selfsupporting. The screen 60 has the overall shape of the mold 50, that is, it has a body 61 which is in the shape of the frustrum of a cone, a head 62 at the smaller end of the body 61, and a flange 63 on the larger end of the body 61, the flange 63 having centric undulations or rolls 64 therein.

The mold 50 is dipped into a tank containing a slurry made up of a water carrier and fibrous materials, such as sulfites, sulfates, cotton, wool, kapok, or the like. Any wood or vegetable fibers may be used, the requisite characteristic being that the fibers be capable of compression. The slurry solution is prepared by stirring and agitating a pulp and water solution to separate the fibers, one from the other. A dye is added to provide the solution with the proper color. The basic'characteristics of the fibers will have an effect on the frequency response of the diaphragm. Softer fibers, such as wool, would result in a lower resonant frequency thanwould harder fibers, such as wood. I

A vacuum pump (not shown) is connected to the opening 52, which vacuum pump is operated to create a partial vacuum within the mold 50, drawing onto the mold a-uniform thickness of the slurry. The mold 50 and the slurry thereon are then withdrawnfrom the tank, with the vacuum pump continuing to operate to dry the slurry. Hot air in'the immediate vicinity of the mold 50 is sucked through the opening 52 to complete the drying'of the slurry and thereby provide a partiallyformed member 70. A blast of air delivered through the opening 52 and oneof the openings 57 blows the mem ber off themold 50 (see FIG. 7). The mold 50-is then used to mold the next member 70. It is to be' understood that a number of techniques may be utilized in mass-producing the member 70 on'such a moldor molds. I

The Iower'surface (as viewed in FIG. 5) of the member 70 conforms precisely to the screen 60. Specifi: cally, the flange 63 inthe screen 60 causes a similarlyshaped flange 72 to be formed in the member 70. The portion of the flange 63 having the rolls 64 therein forms similarly-shaped rolls 72a in the flange 72; and the flat portion of the flange 63 causes the flange 72 also to have a flat portion. The conically-shaped body 61 of the screen 60' causes the body 71 of the member 70'to have a similar shape,'and the head 62 forms a head 73 in the member 70. Although the surface of the member 70 in contact with the screen 60 has the precisely desired final shape, the upper surface is not so well defined, as most clearly seen in FIG. 7. Particularly, it should be noted that the valleys of the rolls on the member 70 are thicker than the peaks.

The next step in making the diaphragm is to apply laquer 75 or other hardening agent to the member 70, preferably to both sides of the member 70. Good results have been attained by dipping the member 70 into the lacquer so as to impregnate the lacquer in the member. Alternatively, the lacquer may be applied in a variety of other ways, such as brushing or spraying. The lacquer 75 will cause the member 70 to retain the compressive forces which are applied in the following step.

In one form of the invention, lacquer of one concentration was applied to the body 71 of the member 70 and lacquer of a different concentration was applied to the flange 72 of the member 70. In this manner, the frequency response of the completed diaphragm may be selected. For example, using a low concentration lacquer on the flange 72 will not significantly increase the resonant frequency. In other words, the compression applied to the flange 72, as described hereinafter, serves to reduce the resonant frequency, and any lacquer applied to the flange 72 would serve to increase the resonant frequency. The amount of increase may be minimized by selecting a lower concentration lacquer, yet achieving water repellancy and the ability to retain the compressive forces. By utilizing a higher concentration lacquer on the body 71, the frequency response in the higher range of frequencies may be controlled. It is to be understood that the invention contemplates a single lacquer or hardening agent, on the one hand, or any number of different hardening agents, on the other, depending upon the exact type of frequency response sought.

Finally, referring to FIG. 9, the member 70 is subjected to pressure by two dies 80 and 90, which dies have mating surfaces that conform precisely to the shape of the final product. Specifically, the dies 80 and 90 respectively have mating undulations 81 and 91 therein conforming precisely to the undulations or rolls that are to be present in the finished product. The lower die 90, in addition to the undulations 91, has a frusto-conical surface 92 and a vertical surface 93, the upper die 80 also having a vertical surface 83. Of course, the portion of the member between the surfaces 83 and 93 will become the apex of the member 70. The undulations 81 and 91 compress the rolls 72a in the flange 72 of the member 70, to give better definition to the valleys and also to decrease the over-all thickness of the rolls, in accordance with the objectives previously explained. The die 80 also includes a relief portion 82, that is, a portion which does not contact, and hence does not compress the member 70. Thus, referring to FIGS. 2-4, the portion between the flange 44 and the circle 48 is not compressed, whereas the flange 44 and the portion of the body 41 between the circle 48 and the apex 42 are compressed. By controlling the extent to which the body 71 of the member 70 is compressed, the frequency response in the higher range of frequencies can be controlled.

The lower die 90 is also provided with a plurality of stops 94 and 95 which serve to limit the extent to which the upper die 80 can compress the member 70. In one form of the invention, the force applied to the upper die 80 was about 2,400 lbs., whereby on a member 70 having 10 square inches of area, the pressure exerted on the member would be about 240 lbs. per square inch. On the other hand, if the area of the member 70 where, say, [00 square inches, the pressure would be 24 lbs. per square inch. By properly adjusting the height of the stops, the final thickness of the product of the member 70 can be selected and the over-all pressure can be adjusted. To achieve the desired definition in the rolls in the flange 72 of the member 70, the pressure should be at least 10 lbs. per square inch and preferably within a range of about 40 lbs. per square inch to 150 lbs. per square inch. It should be clear that the compression of the flange 72 of the member 70 reduces the resonant frequency of the finished diaphragm without lessening the life of the diaphragm or rendering it non-self-supporting.

Preferably, the member 70 is moistened prior to being compressed, and the dies 80 and 90 are heated so as to steam-press the member 70. The finished member is then trimmed, both at the flange and at the neck 73 to provide the diaphragm 40 shown in FIGS. 1-4.

In a diaphragm 40 produced by this method and having an over-all diameter slightly less than 5 V2 inches and having two complete rolls 45, the resonant frequency was about 100 Hz. The application of lacquer or other hardening agent to the flange had the effect of slightly increasing the resonant frequency to about 1 10 Hz.

It is believed that the invention, its mode of construction and assembly, and many of its advantages should be readily understood from the foregoing without further description, and it should also be manifest that, while the preferred embodiment of the invention has been shown and described for illustrative purposes, the structural details are, nevertheless, capable of wide variation within the purview of the invention, as defined in the appended claims.

What is claimed is:

1. A molded loudspeaker diaphragm comprising a body having a frusto-conical shape with a larger end and a smaller end coupled in use to a driver means, and a flange on said larger end, said flange having a flat portion and a roll portion, said flat portion adapted to be I fixedly mounted in use, said flange portion further comprising a lacquer of a first concentration, said body comprising said lacquer of a second concentration, said flange and at least a portion of said body having been laterally compressed under a pressure of at least about 10 pounds per square inch, whereby said roller portion is capable of withstanding extensive flexing thereof as the result of said body being vibrated by the driver means and whereby the response of said diaphragm is improved. 

1. A molded loudspeaker diaphragm comprising a body having a frusto-conical shape with a larger end and a smaller end coupled in use to a driver means, and a flange on said larger end, said flange having a flat portion and a roll portion, said flat portion adapted to be fixedly mounted in use, said flange portion further comprising a lacquer of a fIrst concentration, said body comprising said lacquer of a second concentration, said flange and at least a portion of said body having been laterally compressed under a pressure of at least about 10 pounds per square inch, whereby said roller portion is capable of withstanding extensive flexing thereof as the result of said body being vibrated by the driver means and whereby the response of said diaphragm is improved. 